1. Field of the Invention
The present invention relates to an aromatic polyimide film having an electroconductive metallic surface and a process for the preparation of the same. More particularly, the invention relates to an aromatic polyimide film having a conductive metallic surface which is suitably employed as a circuit printable film which is used for the production of a print circuit board and a process for the preparation of the same.
2. Description of Prior Art
As a circuit printable film having a substrate of an aromatic polyimide which has high heat resistance, a film of three-layer structure (i.e., three-layer film composite) comprising an aromatic polyimide film, an adhesive layer and a metallic copper layer, superposed in order, has been conventionally employed. In this structure, however, when the current is passed in the formed circuit in a fine pattern, the adhesive layer tends to deteriorate because of its low heat resistance, resulting in decrease of adhesion strength.
In view of the above-mentioned problem, a method of directly providing a metal layer on the surface of a resin film without using an adhesive layer has been proposed. For example, Japanese Patent Provisional Publications No. 58(1983)-122939, No. 60(1085)-36666 and No. 60(1985)-36667 disclose a process comprising the steps of preparing a film substrate containing non-conductive metal oxide particles, reducing the surface of the film to convert into a conductive surface, and forming a metal layer on the conductive surface through an electrolytic process.
The employment of the above-mentioned process makes it possible to form a metal layer on a resin film without using an adhesive layer. However, the film composite having a metallic surface obtained by the process is essentially charged with a large amount of metal oxide particles, so that the film composite tends to lower in the mechanical strength and the flexibility. For avoiding these drawbacks, it is considered to decrease the amount of the metal oxide particles to be contained in the film. However, if the amount of the metal oxide particles is reduced, there arises other problem that a metal layer of uniform thickness can be hardly formed on the surface of the film.